Probe molecule studies of CO hydrogenation over Ru/SiO2

Cavalcanti, F.A.P.; Oukaci, R.; Wender, I.; Blackmond, Donna G.

doi:10.1016/0021-9517(90)90174-i

Cited by 12 publications

(3 citation statements)

References 23 publications

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“…13 C 1 probes were also employed to investigate the reactions. Following the pioneering studies by Wender and co-workers and our own earlier work using nitromethane probes, we also measured 13 C NMR spectra of the products obtained on addition of 13 CH 3 NO 2 to a CO hydrogenation over Co/220 °C and over Fe/220 °C. These were quite similar to the spectra obtained using a 13 C 2 H 4 probe at higher temperatures (e.g., Co/220 °C, Figure ) and showed random incorporation and random positioning of 13 C. For example, the central −CH of propene at δ 133.7 showed the presence of propene- 13 C 1 , both propene- 13 C 2 , as well as propene- 13 C 3 isotopomers (Figure and Supporting Information), a result which is completely consistent with random mixing of 13 C from the probe and 12 C from CO.…”

Section: Discussionmentioning

confidence: 99%

Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

et al. 2002

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13C NMR spectroscopy shows that the n-alkene and n-alkane products from the catalytic hydrogenation of CO in the presence of (13)C(2)H(4) probes over Ru/150 degrees C, Co/180 degrees C, Fe/220 degrees C, or Rh/190 degrees C (1 atm, CO:H(2) 1:1, "mild conditions") contain terminal (13)CH(3)(13)CH(2)- units. This is consistent with their formation by a regiospecific polymerization of C(1) species derived from CO and initiated by (13)C(2)H(4). Although the activities toward individual products differed somewhat, similar distributions and similar product labeling patterns were obtained over all the four catalysts. 1-Butene and the higher 1-n-alkenes from all the catalysts were largely (13)CH(3)(13)CH(2)(CH(2))(n)()CH=CH(2) (n = 0-3), propene formed over Ru or Co was (13)CH(3)(13)CH=CH(2), while both (13)CH(3)(13)CH=CH(2) and (13)CH(2)=(13)CHCH(3) were formed over Fe or Rh. Comparison of the conclusions from these probe experiments with those from isotope transient experiments by other workers indicates that the ethene initiator does not significantly modify the course of the CO hydrogenation. The reaction products are largely kinetically determined, and the primary products are mainly linear 1-n-alkenes, while the n-alkanes and 2-n-alkenes largely arise via secondary processes. Since the distribution of products and the labeling in them is so similar, it is concluded that one basic primary mechanism applies over all the four metals. Several different reaction paths involving a polymerization of surface methylene, [CH(2(ad))], have been proposed. Although the predictions based on several of these mechanisms agree with many of the results, the alkenyl + [CH(2(ad))] mechanism, initiated by a surface vinyl [CH(2)=CH((ad))], most easily accommodates the experimental evidence. An alternative path involving sequential addition of surface methylidyne and hydride either to a growing alkylidene chain (alkylidene + [CH(ad) + H(ad)]) or to an alkyl chain (alkyl + [CH((ad)) + H(ad)]) has recently been proposed by van Santen and Ciobica. The [CH(2(ad))] mechanism offers an easier explanation for the formation of the various alkenes, the distribution of products, and of the initiation, while the [CH(ad) + H(ad)] mechanism can explain any n-alkanes formed as primary products and not derived from alkenes. At higher reaction temperatures over Ru and Co, considerable (13)C(1) incorporation (from natural abundance in the CO and from cleavage of the (13)C(2)H(4) probe) was found in all the hydrocarbons. Thus, at higher temperatures (13)C(1(ad)) in addition to (13)C(2(ad)) species participate in both chain growth and initiation. In summary, adsorbed CO is transformed very easily into surface C(1(ad)), probably [CH(2(ad))] in equilibrium with [CH((ad))+H(ad)], which act as the propagating species.

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Section: Discussionmentioning

confidence: 99%

Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

et al. 2002

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“…In our recent studies on the mechanism of the hydrogenation of carbon monoxide to alkenes (the Fischer−Tropsch reaction) using 13 C 2 -labeled probe molecules over rhodium, ruthenium, and cobalt catalysts, we have found that the 13 C labels in the products are consistent with a process involving the reactions of surface methylenes with surface alkenyl (rather than alkyl) species . We now report, (i) that both diazomethane and nitromethane can be effective C 1 probes and (ii) that while methylenes derived from 13 CH 2 N 2 or 13 CH 3 NO 2 probes and methylenes formed from 12 CO hydrogenation combine randomly over cobalt (giving products containing mixtures of 12 C and 13 C atoms), quite separate reactions occur over rhodium Fischer−Tropsch catalysts.…”

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confidence: 60%

Carbon Monoxide Hydrogenation: Intermediates Derived from Methylene Probes Offering Dual Polymerization Pathways in Fischer−Tropsch Homologation

et al. 1996

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“…These Cl reaction intermediates can also be formed from other molecules than CO. Petit and Brady [13,14] used CH2N2 as a source for surface carbon, Cavalcanti et al [15,16] used CH3N02, Van Barneveld and Ponec [17] used CH(4-x)Cl x and Williams et al [18] demonstrated that also surface carbon. generated from methyliodide could be incorporated into C2+ hydrocarbons during CO hydrogenation.…”

Section: Introductionmentioning

confidence: 99%

Reaction Routes for Methane Conversion on Transition Metals at Low Temperature

Koerts

Santen

1993

Studies in Surface Science and Catalysis

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Probe molecule studies of CO hydrogenation over Ru/SiO2

Cited by 12 publications

References 23 publications

Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

Carbon Monoxide Hydrogenation: Intermediates Derived from Methylene Probes Offering Dual Polymerization Pathways in Fischer−Tropsch Homologation

Reaction Routes for Methane Conversion on Transition Metals at Low Temperature

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Probe molecule studies of CO hydrogenation over Ru/SiO2

Cited by 12 publications

References 23 publications

Investigations by 13C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

Investigations by 13C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

Carbon Monoxide Hydrogenation: Intermediates Derived from Methylene Probes Offering Dual Polymerization Pathways in Fischer−Tropsch Homologation

Reaction Routes for Methane Conversion on Transition Metals at Low Temperature

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Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

Investigations by ¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation